Renthal Sprockets Kit - Grooved Countershaft Sprocket - Blue TwinRing Rear Sprocket - Compatible with: Yamaha WR426F ( 2001 to 2002 ) & Yamaha WR450F ( 2003 to 2021 ) Compatible with: Yamaha YZ250 ( 1999 to 2021 ) [ Two Stroke ] & Yamaha YZ250X ( 2016 to 2021 ) [ Two Stroke ] Compatible with: Yamaha YZ426F ( 2000 to 2002 ) & Yamaha YZ450F ( 2003 to 2021 ) + Yamaha YZ450FX ( 2017 to 2021 ) Orders cannot be canceled or changed once they are sent to the warehouse. Any order update information is sent to your Amazon email address. Renthal Sprockets Chain Kit - Grooved Front Countershaft Sprocket & Blue Twinring Rear Sprocket. FRONT COUNTERSHAFT SPROCKET:. Renthal Front Chainwheels are simply the finest front chainwheel on the market today. Their Front Chainwheels feature a specially developed Nickel-Chrome-Molybdenum steel which is case hardened and core refined to give the ultimate combination of strength and hardness. Precision CNC Machined to extremely tight tolerances. . Case hardened and core refined 655M13 Nickel-Chrome-Molybdenum alloy steel to give the ultimate combination of strength and hardness. . Self-cleaning mud grooves between every tooth on both sides help prevent dirt build up. TWINRING REAR SPROCKET:. Unique flat face design keeps weight to a minimum and means the TwinRing is as narrow as a regular chainwheel Inner Ring is high strength Ultralight 7075 T6 Aluminum. Outer Ring is Electroless Nickel Coated steel Outer is expanded at 200C and then fitted to inner, creating a permanent bond for the life of the sprocket Precision CNC machined to extremely tight tolerances Flat socket head screws add additional strength to the chainwheel during side impacts Self-cleaning mud grooves between every tooth on both sides help prevent dirt build up .